This invention relates to a hydraulic control device for incorporation in a hydraulic control system for a mine roof support assembly.
A known hydraulic control system (see U.S. Pat. No. 3,821,880) has a rotary slide valve which controls a group of hydraulically-actuatable directional control valves, each of which is allocated to a respective hydraulic ram of the time roof support units, the working chambers of the rams being connected to the output sides of the directional control valves. The input side of the rotary slide valve is connected to hydraulic pressure and return lines; and its output side is connected, via hydraulic control lines, to the directional control valves. This type of control system, with its manually-operable slide valve, is intended for manual control, or for combined manual and automatic control.
In the course of the further development and automation of control systems of this type, electrohydraulic control systems have become known (see U.S. Pat. No. 4,378,027), in which, in place of the rotary slide valve, a magnetic valve is used as a pre-control valve. Such a magnetic valve is actuatable electrically from a central control position, or by a electronic control system associated with the roof support assembly. In this way, it is possible to control the various working actions of the assembly such as prop robbing and setting, conveyor and roof support advance etc. Such a control system, when used in a modern support assembly, requires a relatively large number of magnetic valves, and this results in an expensive system.
The aim of the invention is to provide a hydraulic control device for incorporation in a hydraulic control system for a mine roof support assembly, which device avoids the high expense resulting from the use of a costly rotary slide valve or from a plurality of costly magnetic valves.